Etching Maximizes the Sun's Rays

March 17, 2015

Chuck Black displays a nanotextured square of silicon on top of an ordinary silicon wafer. The nanotextured surface is completely antireflective and could boost the production of solar energy from silicon solar cells.

Reducing the amount of sunlight that bounces off the surface of solar cells helps maximize the conversion of the sun's rays to electricity, so manufacturers use coatings to cut down on reflections. Now scientists at the U.S. Department of Energy's Brookhaven National Laboratory show that etching a nanoscale texture onto the silicon material itself creates an antireflective surface that works as well as state-of-the-art thin-film multilayer coatings.

Their method has potential for streamlining silicon solar cell production and reducing manufacturing costs. The approach may find additional applications in reducing glare from windows, providing radar camouflage for military equipment, and increasing the brightness of light-emitting diodes.

"For antireflection applications, the idea is to prevent light or radio waves from bouncing at interfaces between materials," said physicist Charles Black, who led the research at Brookhaven Lab's Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility.

Preventing reflections requires controlling an abrupt change in "refractive index," a property that affects how waves such as light propagate through a material. This occurs at the interface where two materials with very different refractive indices meet, for example at the interface between air and silicon. Adding a coating with an intermediate refractive index at the interface eases the transition between materials and reduces the reflection, Black explained. "The issue with using such coatings for solar cells," he said, "is that we'd prefer to fully capture every color of the light spectrum within the device, and we'd like to capture the light irrespective of the direction it comes from. But each color of light couples best with a different antireflection coating, and each coating is optimized for light coming from a particular direction. So you deal with these issues by using multiple antireflection layers. We were interested in looking for a better way."

Nanoscale Mirrored Cavities Amplify, Connect Quantum Memories

March 17, 2015

Building quantum memories on a chip: Diamond photonic crystal cavities (ladder-like structures) are integrated on a silicon substrate. Green laser light (green arrow) excites electrons on impurity atoms trapped within the cavities, picking up information about their spin states, which can then be read out as red light (red arrow) emitted by photoluminescence from the cavity. The inset shows the nitrogen-vacancy (NV)-nanocavity system, where a nitrogen atom (N) is substituted into the diamond crystal lattice in place of a carbon atom (gray balls) adjacent to a vacancy (V). Layers of diamond and air keep light trapped within these cavities long enough to interact with the nitrogen atom's spin state and transfer that information via the emitted light. Photo credit: MIT

The idea of computing systems based on controlling atomic spins just got a boost from new research performed at the Massachusetts Institute of Technology (MIT) and Brookhaven Lab’s Center for Functional Nanomaterials (CFN). By constructing tiny "mirrors" to trap light around impurity atoms in diamond crystals, the team dramatically increased the efficiency with which photons transmit information about those atoms' electronic spin states, which can be used to store quantum information. Such spin-photon interfaces are thought to be essential for connecting distant quantum memories, which could open the door to quantum computers and long-distance cryptographic systems.

Crucially, the team demonstrated a spin-coherence time (how long the memory encoded in the electron spin state lasts) of more than 200 microseconds—a long time in the context of the rate at which computational operations take place. A long coherence time is essential for quantum computing systems and long-range cryptographic networks.

"Our research demonstrates a technique to extend the storage time of quantum memories in solids that are efficiently coupled to photons, which is essential to scaling up such quantum memories for functional quantum computing systems and networks," said MIT's Dirk Englund, who led the research. Scientists at the CFN helped to fabricate and characterize the materials.

To learn more about this advance that could lead to quantum computing and the secure transfer of information over long-distance fiber optic networks visit: www.bnl.gov/newsroom/news.php?a=11695

Long Island Regional Science Bowl Results

March 17, 2015

Farmingdale High School Team with Energy Secretary Moniz

Recently, Brookhaven Lab hosted the High School and Middle School Long Island Regional Science Bowls. On Saturday, January 31, fifteen teams participated in one of the nation's regional competitions of the 25th Annual U.S. Department of Energy National Science Bowl® (NSB). In an exciting finish, Farmingdale edged out Great Neck South High School to win the competition. Last year's top team, Ward Melville High School, took third place, and Longwood High School was the fourth-place division winner.

The 10th annual Middle School Science Bowl was held at the Lab on Saturday, March 7. About 100 students on 19 teams participated in the competition. After nine rounds, Robert Cushman Murphy Junior High School, Stony Brook, emerged victorious. Commack Middle School placed second in the "Jeopardy-style" academic contest and John F. Kennedy Middle School of Port Jefferson Station placed third. Four divisions compete in the initial round-robin eliminations, of which J. Taylor Finley Middle School of Huntington took the top spot in their division.

Robert Cushman Murphy Junior High School Team

"The National Science Bowl® has grown into one of the most prestigious science academic competitions in the country and challenges students to excel in fields vital to America's future," U.S. Energy Secretary Ernest Moniz said. "I congratulate these students for advancing to the National Finals, where they will be among some of the brightest science and math students from across the country."

The winning teams will be awarded all-expenses-paid trips to the National Finals in Washington, D.C., scheduled for April 30-May 4.

Happenings

April 22 – Noon Recital. Stony Brook Opera. David Lawton presents a preview of the semi-staged concert Gaetano Donizetti’s Lucia di Lammermoor to be performed at Stony Brook on April 25/26. Berkner Hall Auditorium.

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